查看更多>>摘要：A designed Mg88.7Ni6.3Y5 hydrogen storage alloy containing 14H type LPSO(long-period stacking ordered)and ternary eutectic structure was prepared by regulating the alloy composition and casting.The hydrogen storage performance of the alloy was improved by adding nanoflower-like TiO2@C catalyst.The decomposition of the LPSO structure during hydrogenation led to the formation of plenty of nanocrystals which pro-vided abundant interphase boundaries and activation sites.The nanoscale TiO2@C catalyst was uniformly dispersed on the surface of alloy par-ticles,and the"hydrogen overflow"effect of TiO2@C accelerated the dissociation and diffusion of hydrogen on the surface of the alloy parti-cles.As a result,the in-situ endogenous nanocrystals of the LPSO structure decomposition and the externally added flower-like TiO2@C cata-lyst uniformly dispersed on the surface of the nanoparticles played a synergistic catalytic role in improving the hydrogen storage performance of the Mg-based alloy.With the addition of the TiO2@C catalyst,the beginning hydrogen desorption temperature was reduced to 200 ℃.Further-more,the saturated hydrogen absorption capacity of the sample was 5.32％,and it reached 4.25％(mass fraction)H2 in 1 min at 200 ℃ and 30 bar.
查看更多>>摘要：This study investigates the effect of characteristics and distribution of Mg17Al12 precipitates on the uniaxial tensile and three-point bending properties of extruded Mg alloys containing high Al contents.The extruded Mg-9Al-1Zn-0.3Mn(AZ91)alloy contains lamellar-structured Mg17Al12 discontinuous precipitates along the grain boundaries,which are formed via static precipitation during natural air cooling.The extruded Mg-11Al-1Zn-0.3Mn(AZ111)alloy contains spherical Mg17Al12 precipitates at the grain boundaries and inside the grains,which are formed via dynamic precipitation during extrusion.Due to inhomogeneous distribution of precipitates,the AZ111 alloy consists of two different precipitate regions: precipitate-rich region with numerous precipitates and finer grains and precipitate-scarce region with a few precipitates and coarser grains.The AZ111 alloy exhibits a higher tensile strength than the AZ91 alloy because its smaller grain size and more abundant precipitates re-sult in stronger grain-boundary hardening and precipitation hardening effects,respectively.However,the tensile elongation of the AZ111 alloy is lower than that of the AZ91 alloy because the weak cohesion between the dynamic precipitates and the matrix facilitates the crack initiation and propagation.During bending,a macrocrack initiates on the outer surface of bending specimen in both alloys.The AZ111 alloy exhibits higher bending yield strength and lower failure bending strain than the AZ91 alloy.The bending specimens of the AZ91 alloy have similar bending formability,whereas those of the AZ111 alloy exhibit considerable differences in bending formability and crack propagation behavior,depending on the distribution and number density of precipitates in the specimen.In bending specimens of the AZ111 alloy,it is found that the failure ben-ding strain(εf,bending)is inversely proportional to the area fraction of precipitates in the outer zone of bending specimen(Appt),with a relationship of εf,bending=-0.1Appt+5.86.
查看更多>>摘要：The effects of nano-CaO contents on the microstructure,mechanical properties and corrosion resistance of lean Mg-1Zn alloy were investiga-ted.The results showed that the addition of nano-CaO significantly refined the grain size and improved mechanical properties of the Mg-1Zn al-loy.At the same time,CaO reacted with molten Mg in situ to form nano-MgO,whose corrosion product in SBF solution was the same with the degradation product of Mg matrix,resulting in the enhanced compactness of the Mg(OH)2 layer and reduced corrosion rate of matrix.The Mg-1Zn alloy had lower corrosion resistance due to excessively large grain size and shedding of corrosion products.The composite with 0.5％(mass fraction)CaO had the best corrosion resistance with a weight loss of 9.875 mg·a-1·mm-2 due to the small number of Ca2Mg6Zn3 phase and suitable grain size.While for composites with high content of CaO(0.7％and 1.0％,in mass fraction),they had lower corrosion re-sistance due to the coexistence of large number of Ca2Mg6Zn3 and Mg2Ca at grain boundaries,especially for 1.0％CaO composite,resulting from the strong micro-galvanic corrosion.
查看更多>>摘要：In an effort to clarify the formation mechanism of LPSO structure in Mg-Y-Zn alloy,the chemical environment and structural ordering in liq-uid Mg-rich Mg-Y-Zn system are investigated with the aid of ab-initio molecular dynamics simulation.In liquid Mg-rich Mg-Y alloys,the strong Mg-Y interaction is determined,which promotes the formation of fivefold symmetric local structure.For Mg-Zn alloys,the weak Mg-Zn interaction results in the fivefold symmetry weakening in the liquid structure.Due to the coexistence of Y and Zn,the strong attractive interac-tion is introduced in liquid Mg-Y-Zn ternary alloy,and contributes to the clustering of Mg,Y,Zn launched from Zn.What is more,the distribu-tion of local structures becomes closer to that in pure Mg compared with that in binary Mg-Y and Mg-Zn alloys.These results should relate to the origins of the Y/Zn segregation zone and close-packed stacking mode in LPSO structure,which provides a new insight into the formation mechanism of LPSO structure at atomic level.
查看更多>>摘要：Mg-air batteries have attracted tremendous attention as a potential next-generation power source for portable electronics and e-transportation due to their remarkable high theoretical volumetric energy density,environmental sustainability,and cost-effectiveness.However,the fast hydro-gen evolution reaction(HER)in NaCl-based aqueous electrolytes impairs the performance of Mg-air batteries and leads to poor specific capaci-ty,low energy density,and low utilization.Thus,the conventionally used NaCl solute was proposed to be replaced by NaNO3 and acetic acid ad-ditive as a corrosion inhibitor,therefore an electrolyte engineering for long-life time Mg-air batteries is reported.The resulting Mg-air batteries based on this optimized electrolyte demonstrate an improved discharge voltage reaching about 1.8 V for initial 5 h at a current density of 0.5 mA ·cm-2 and significantly prolonged cells'operational lifetime to over 360 h,in contrast to only about 17 h observed in NaCl electrolyte.X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were employed to analyse the composition of surface film and scanning electron microscopy combined with transmission electron microscopy to clarify the morphology changes of the surface layer as a func-tion of acetic acid addition.The thorough studies of chemical composition and morphology of corrosion products have allowed us to elucidate the working mechanism of Mg anode in this optimized electrolyte for Mg-air batteries.
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